Electrowetting is an interfacial effect in which the contact angle of a polar liquid on a surface may be changed by applying a voltage between the liquid and that surface. The use of liquid lenses, in which the shape of an interface between a polar liquid and a non-polar liquid is controlled by electrowetting to provide optical focusing and optical stabilization functions, has been proposed for cellphones as well as a range of other applications, including barcode readers, surveillance and traffic cameras and medical & military applications, as such lenses are compact in size, robust in design and respond quickly enough to remove hand jitter artifacts. However, the one-at-a-time approach used to date to manufacture liquid lenses has inhibited their widespread implementation in cost-sensitive fields, as it necessarily keeps costs high in relation to more conventional batch-fabricated glass and plastic lenses.
One major problem encountered in manufacturing any liquid lens is the difficulty of making reliable bonds between the component parts in the presence of the liquids involved, one of which typically includes water. Another problem is the liquid expansion that occurs when the fully fabricated liquid lens is raised from room temperature to maximum allowed shipping temperature (e.g. 85° C.) for testing prior to shipping, a standard requirement for consumer products. The liquid expansion can stress those bonds, weakening them up to the point of leakage or failure. An additional problem arises when trying to transition from one-at-a-time to wafer scale assembly of liquid lenses, because fabricating at least one of the essential component parts (a part including substantially conical or other axisymmetrically shaped through holes necessary for liquid confinement) on a wafer scale with the necessary surface profiles and smoothness is difficult and expensive when traditional materials such as aluminum or stainless steel are used for those parts.
It is therefore desirable to provide a method for making arrays of liquid lenses using wafer scale fabrication, employing bonding techniques that work in the presence of liquids, using materials that lend themselves to low-cost but high-precision fabrication, and using designs that accommodate the expected thermal excursions with minimal risk of structural failure. Ideally, the fabrication method would include a simple convenient way to provide the electrical connections required to apply external voltage to manipulate the meniscus and so control the focal length of the lens.